1. Field of the Invention
The present invention relates to opposing field spectrometers of the type which may be utilized to undertake measurements utilizing an electron beam probe.
2. Description of the Prior Art
The use of a spectrometer having an electrion beam probe to conduct voltage measurements at various test points on the surface of a specimen, such as voltage measurement at tracks and nodes of integrated microelectronic components, is becoming wide spread.
In such an electron beam test installation, the test points to be measured on a specimen surface are irradiated with primary electrons causing the release or emission of secondary electrons. Depending upon the voltage which is present at the test point, the energy distribution function of the secondary electrons is altered. This change in the energy distribution function of the secondary electrons can be determined in a spectrometer for such secondary electrons, and thus the voltage which is present at the test point can be ascertained. A spectrometer which may be utilized in such an electron beam test installation is described in the article "VLSI Testing Using the Electron Probe", by H. P. Feuerbaum, Scanning Electron Microscopy/1979/I, at pages 285-296. The spectrometer described therein, however, cannot transmit the entire solid angle distribution of the secondary electrons emitted at the test point, thus causing a measuring error in the range of 5% to 10%. This measuring error primarily results from the fact that an electron obliquely approaching the planar opposing field network or electrode with a specific energy may, under certain conditions, no longer pass the opposing field lattice, whereas an electron of the same energy moving perpendicularly relative to the opposing field network may still have enough energy to minimally pass the opposing field network.
The general concept of a spherical network in other types of spectrometers is described in, for example, the article by C. J. Workowski in the Journal of Physics, E13(1980) beginning at page 67.